Variable resolution scanning in line scan optical imaging systems

Abstract

An improvement to a facsimile system which enables the simulation of 240 and 300 DPI feedwise scan resolutions in a system designed to operate at 200 and 400 DPI feedwise scan resolutions. The simulation is accomplished by feedwise advancing a document past a horizontal image scanner in defined sequences of half and full steps, half steps causing the document to be feedwise advanced by one four-hundredth of an inch (as in 400 DPI mode), full steps causing the document to be feedwise advanced by one two-hundredth of an inch (as in 200 DPI mode). The scan resolution errors introduced by the simulation are non-cumulative since the system comes back into feedwise synchronization with true 240 and 300 DPI scan resolutions each time one of the defined three operation sequences is completed. Also, a method of operating a document feeding system to approximate 240 and 300 DPI feedwise scan resolutions.

What is claimed is: 
     
       1. A method of operating a document feeding system to approximate a 240 DPI feedwise scan resolution, said system including means for feedwise advancing said document by either one four-hundredth of an inch or one two-hundredth of an inch, said method comprising the steps of: a--advancing said document by said one two-hundredth of an inch;   b--advancing said document by said one four-hundredth of an inch;   c--advancing said document by said one two-hundredth of an inch; and   d--repeating said steps a-c.   
     
     
       2. The method in accordance with claim 1 further including the step of scanning a scanwise section of said document while said document is being feedwise advanced. 
     
     
       3. The method in accordance with claim 1 wherein said system includes driving means for feedwise advancing said document, said driving means operable in full steps or half steps, one of said full steps causing said document to be feedwise advanced by said one two-hundredth of an inch, one of said half steps causing said document to be feedwise advanced by said one four-hundredth of an inch, said steps a and c accomplished by operating said driving means for one of said full steps, said step b accomplished by operating said driving means for one of said half steps. 
     
     
       4. The method in accordance with claim 3 wherein said driving means includes a stepper motor, the rotation of said stepper motor causing said document to be feedwise advanced in direct relation to the degrees of stepper motor rotation, said stepper motor rotated by a fixed number of degrees for each of said full steps, said stepper motor rotated by half of said fixed number of degrees for each of said half steps. 
     
     
       5. A method of operating a document feeding system to approximate a 300 DPI feedwise scan resolution, said system including means for feedwise advancing said document by either one four-hundredth of an inch or one two-hundredth of an inch, said method comprising the steps of: a--advancing said document by said one four-hundredth of an inch;   b--advancing said document by said one two-hundredth of an inch;   c--advancing said document by said one four-hundredth of an inch; and   d--repeating said steps a-c.   
     
     
       6. The method in accordance with claim 5 further including the step of scanning a scanwise section of said document while said document is being feedwise advanced. 
     
     
       7. The method in accordance with claim 5 wherein said system includes driving means for feedwise advancing said document, said driving means operable in full steps or half steps, one of said full steps causing said document to be feedwise advanced by said one two-hundredth of an inch, one of said half steps causing said document to be feedwise advanced by said one four-hundredth of an inch, said step b accomplished by operating said driving means for one of said full steps, said steps a and c accomplished by operating said driving means for one of said half steps. 
     
     
       8. The method in accordance with claim 7 wherein said driving means includes a stepper motor, the rotation of said stepper motor causing said document to be feedwise advanced in direct relation to the degrees of stepper motor rotation, said stepper motor rotated by a fixed number of degrees for each of said full steps, said stepper motor rotated by half of said fixed number of degrees for each of said half steps. 
     
     
       9. A system including illuminating means for illuminating a document, lens means for focusing light reflected from a scanwise line onto a scanner means, and means for feedwise advancing said document in increments of one four-hundredth of an inch or one two hundredth of an inch, said scanner means for reading said focused reflected light while said document is being feedwise advanced, wherein the improvement comprises: control means, connected to said feedwise advancing means, for causing said document to be feedwise advanced past said scanwise line in a first sequence of steps of one two-hundredth of an inch, one four-hundredth of an inch, and one two-hundredth of an inch, whereby a 240 DPI feedwise scanning resolution is approximated.   
     
     
       10. The facsimile system in accordance with claim 9 wherein said control means further includes means for repeating said first sequence so long as said document is to be scanned at said approximate 240 DPI feedwise scanning resolution. 
     
     
       11. The system in accordance with claim 9 wherein said control means further includes means for causing said document to be feedwise advanced in a second sequence of steps of one four-hundredth of an inch, one two-hundredth of an inch, and one four-hundredth of an inch, whereby a 300 DPI feedwise scanning resolution is approximated. 
     
     
       12. The system in accordance with claim 9 wherein said feedwise advance means includes: a stepper motor; and   drive means, responsive to the output of said stepper motor, for feedwise advancing said document in direct proportion to the rotation of said stepper motor.   
     
     
       13. The system in accordance with claim 12 wherein said stepper motor, in response to said control means, will rotate by a full motor step or a half motor step, said full motor step corresponding to the rotation of said stepper motor by a fixed number of degrees, said half motor step corresponding to rotation of said stepper motor by half of said fixed number of degrees, said full motor step causing said drive means to feedwise advance said document by one two-hundredth of an inch, said half motor step causing said drive means to feedwise advance said document by one four-hundredth of an inch. 
     
     
       14. A system including illuminating means for illuminating a document, lens means for focusing light reflected from a scanwise line onto a scanner means, and means for feedwise advancing said document in increments of one four-hundredth of an inch or one two hundredth of an inch, said scanner means for reading said focused reflected light while said document is being feedwise advanced, wherein the improvement comprises: control means connected to said feedwise advancing means, for causing said document to be feedwise advanced past said scanwise line in a first sequence of steps of one four-hundredth of an inch, one two-hundredth of an inch, and one four-hundredth of an inch, whereby a 300 DPI feedwise scanning resolution is approximated.   
     
     
       15. The system in accordance with claim 14 wherein said control means further includes means for repeating said first sequence so long as said document is to be scanned at said approximate 300 DPI feedwise scanning resolution. 
     
     
       16. The system in accordance with claim 14 wherein said control means further includes means for causing said document to be feedwise advanced in a second sequence of steps of one two-hundredth of an inch, one four-hundredth of an inch, and one two-hundredth of an inch, whereby a 240 DPI feedwise scanning resolution is approximated. 
     
     
       17. The system in accordance with claim 14 wherein said feedwise advance means includes: a stepper motor; and   drive means, responsive to the output of said stepper motor, for feedwise advancing said document in direct proportion to the rotation of said stepper motor.   
     
     
       18. The system in accordance with claim 17 wherein said stepper motor, in response to said control means, will rotate by a full motor step or a half motor step, said full motor step corresponding to the rotation of said stepper motor by a fixed number of degrees, said half motor step corresponding to rotation of said stepper motor by half of said fixed number of degrees, said full motor step causing said drive means to feedwise advance said document by one two-hundredth of an inch, said half motor step causing said drive means to feedwise advance said document by one four-hundredth of an inch. 
     
     
       19. The facsimile system in accordance with claim 14 wherein said focusing means and said scanner means are capable of resolving a 400 feedwise DPI scan resolution.